Tubular reactor and method

ABSTRACT

In a tubular reactor (2) for catalytic chemical gas-phase reactions with symparallel [sic] guidance of the heat-exchanger, a partial stream of the heat-exchanger medium, this partial stream immediately neighboring the inlet side of the tube plate (6), is introduced through a by-pass channel (26) arranged in the center of the bank of tubes (4), by-passing the bank of tubes, and introduced at a point which is downstream to the discharge area of the heat-exchanger. In this way, undersirable severe local cooling in the reaction area of the bank of tubes (4) can be avoided.

The invention is concerned with a tubular reactor according to the mainconcept of claim 1.

Such tubular reactors represent a frequently desired and many timesunavoidable structural and operational form of large chemical reactors.They can be designed with parallel, radial, transverse flow ordouble-transverse flow heat-exchanger, where the main directional flowin the heat-exchanger, produced by components such as deflectors and/ordistributor plates, is defined with respect to the reactor tubes. In allcases, the heat-exchange medium entering the reactor housing is forcedso that a substantial part will follow a path first along the tube plateor separator plate. With increasing length of the respective transverseflow and with increasing temperature difference there between thereaction gas and heat-exchanger, the problem, that the portion of theheat-exchange medium that flows more or less directly along the tubeplate or separating plate will be cooled down to an undesirably greatextent, becomes more severe. This is understandable if one keeps in mindthat, for example, the reaction gas entering there may have atemperature of 100° or 150° C., while the reaction temperature and,consequently the temperature of the heat exchanger, is 400° C. Thetemperature differences between the various layers of the heat-exchangerthat are produced by the disproportionately strong cooling mentionedabove will remain to some extent even during the rest of the flow andwill therefore lead to different temperatures and different temperatureprofiles at the individual contact tubes, and this may result in anadverse influence on yield and selectivity. An attempt to reduce thesetemperature differences by increasing the flow velocity of theheat-exchanger medium would result in a disproportionately largeincrease of pump performance and thus energy consumption.

Therefore, the task of the invention is to create a tubular reactoraccording to the main concept, in such a way that the temperatures andtemperature profiles of the individual contact tubes can be keptapproximately equal without this requiring a significant increase inpump power.

According to the invention, this task is solved by the characterizingpart of claim 1. The Subclaims give further advantageous modes ofexecution.

The purpose of the by-pass channel is that, the portion of theheat-exchange medium which is cooled disproportionately strongly at thetube plate or separating plate near the inlet is guided directly to nearthe outlet region of the heat-exchange medium or at least to a pointnear to this within the reactor housing, by by-passing the contact tubesas well as other flow-conducting structural parts, such as deflectorplates and distributor plates, and there its relatively low temperatureis harmless or even desirable. For example, this area can be at theheight of the hot spot and there again inside a deflector plateextending inward.

The construction of the by-pass channel according to the invention issimple. It requires a free space in the middle of the bank of tubes, butsuch a space is expedient anyway in the case of large reactors forflow-technological reasons, as presented in DE Patent 25 59 661.

Below, some modes of execution of the tubular reactors according to theinvention will be described in more detail, with the aid of drawings.

FIG. 1 shows a vertical tubular reactor with cylindrical tubes, shownschematically as the longitudinal cross-section, with the reaction gasand heat-exchange medium entering at the lower end.

FIG. 2 is a similar representation of the tubular reactor with twogroups of opposing tubes and double transverse flow of the heat-exchangemedium.

FIGS. 3 and 4 each show a schematic cross-section of the reactoraccording to FIG. 2, approximately at the height of line A--A, withdifferent designs of the by-pass channel and

FIG. 5 is again a similar representation to FIG. 1 of a tubular reactorwith a cylindrical bank of tubes, whereby the space for theheat-exchanger in the reactor housing is of course divided by aseparator into two superimposed separated sections, corresponding tohighly different heat-exchange requirements.

The tubular reactor 2, shown in FIG. 1, contains a cylindrical bank ofreaction tubes 4 which ends in tube plates 6 and 8. The reaction gas isintroduced to the bank of tubes 4 from the bottom through a hood 10,while a similar upper hood 12 collects the reacted gas that leaves thebank of tubes. The inner space of reactor 2 between tube plates 6 and 8is filled, outside the bank of tubes 4, with a heat-exchange medium, forexample, a salt melt, which surrounds the tubes. This medium isintroduced into reactor housing 14 near the lower tube plate 6, radiallythrough an annular channel 16 and is discharged near upper tube plate 8through an annular channel 18, and then into the heat-exchanger which isoutside the reactor and is not shown. Between the two tube plates 6 and8, the heat-exchange medium is forced to flow in a meandering manneraround deflecting plates 20 and 22 in various planes in order to passaround the bank of tubes, substantially in the form of a "transverseflow", that is, radially in this case. Deflecting plates 20 and 22usually have openings for the individual tubes but leaving a gap betweenthe plate and the tube and these individual gaps can be dimensioned insuch a way that they regulate the part of the stream of theheat-exchange medium that can pass through them in the axial directionof the reactor, in order to provide to the bank of tubes 4 a desiredtemperature field. Reactor 2 is of such a type that it allows inside thebank of tubes 4 a coaxial cylindrical space that does not contain anycontact tubes.

While the mean reaction temperature in the bank of tubes 4 and thus alsothe temperature of the heat-exchange medium is, for example, at about400° C., regardless of whether the reaction is exothermic orendothermic, the reaction gas enters through the hood 10 into the bankof tubes at a temperature of approximately 100° C. Naturally, as aresult of this, the lower tube plate 6 is cooled considerably and thiscooling effect is also imparted to the layers of the heat-exchangemedium neighboring it.

Since these layers are not at rest, but form a partial stream, asindicated by arrows 24, normally, this undercooled partial stream coolsthe bank of tubes at the points that cannot be controlled satisfactorilyto temperatures which are harmful to the course of the reaction.

In order to prevent this, now, in reactor 2 shown here, for which aby-pass channel 26 is provided for the partial stream indicated witharrow 24; in this case, the by-pass channel consists of a coaxial tube28 with funnel-like expansions 30 and 32 at the two ends near tubeplates 6 and 8, respectively. The partial stream of the heat-exchangemedium designated by arrows 24 will be introduced into this by-passchannel 26 directly from the outlet end of the bank of tubes 4, withoutbeing able to come into contact further with the bank of tubes. At theoutlet end of the bank of tubes 4, near tube plate 8, this partialstream flows outward according to arrows 34, to annular channel 18,approximately in the same way as it did from annular channel 16 to thecenter of the bank of tubes. It can be assumed that the reaction iscompleted at the discharge end of bank of tubes 4 and that thereenhanced cooling of the reacted gases is desirable anyway.

In order to improve the flow of the said partial stream in and throughpipe 28, the cylindrical peripheral inlet cross-section between tubeplate 6 and enlarged part 32 can be covered with a sieve-like perforatedplate 36, as shown.

FIG. 2 shows a tubular reactor 40, which, instead of a hollowcylindrical bank of tubes according to FIG. 1, consists of two groups ofbank of tubes 42 and 44, set opposite to one another at a distance and,correspondingly, the heat-transfer medium which enters from the oppositesides flows through them in what is called a double transverse flow,while otherwise the internal construction with alternating deflectionplates 46 and 48 corresponds in principle to that shown in FIG. 1.

Now, in this case, a by-pass channel 50 is arranged in the space betweenthe two groups of bank of tubes, 42 and 44. FIGS. 3 and 4 show twodifferent modes of execution of these.

According to FIG. 3, the by-pass channel 50 consists substantially of abox-like guide channel 52, which extends over the entire width ofreactor 40, and, according to FIG. 4, of a row of individual pipes 54.In each case, again enlargements can be provided at both ends, similarlyto enlargements 30 and 32 in FIG. 1, and also in order to achieve betterflow, a perforated plate similar to perforated plate 36 may be locatedat the inlet cross-section.

Reactor 60 according to FIG. 5 is again similar to that of FIG. 1 andhas a hollow cylindrical bank of tubes 62 and annular channels 64 to 70.However, in this case, the reactor housing 72 is subdivided into twosuperimposed heat-exchanger sections 76 and 78, which are at leastsubstantially separated from one another, by a separator plate 74through which the bank of tubes passes, as it is shown approximately thesame way in DE-OS 2,201,528. Similarly, here, for example, instead ofthe alternating deflector plates 20 and 22, in heat-exchanger section78, continuous [passing through] distributor plates 80 with annular gapsaround the individual reactor tubes are provided between the respectiveannular channel 68 and 70 in the immediate neighborhood of these.Through these distributor plates, the flow of the heat-exchange mediumwill become substantially directed in the axial direction. However, thisdoes not change the situation at all that a partial stream of theheat-exchange medium entering through the respective annular channel 68will undergo an undesirably severe temperature change as a result of theseparator plate, namely the partial stream, which passes in theimmediate neighborhood of separator plate 74. For this reason, again aby-pass channel 82 is provided, which is in the form of a central tube84 that is enlarged on both sides, as it was done in the case of reactor2 according to FIG. 1.

Similarly, the heat-exchanger section 76 under it has a central tube 86,but, in this example, this is surrounded coaxially, at a distance, byanother tube 88, in order to provide two separate by-pass channels, 90and 92. In this way, the partial stream of the heat-exchanger,designated by arrows 94 and 96, can be removed from the area of thelower tube plate 98 in layers, whereby one must assume that the partwhich goes through the gap between guide tubes 86 and 88 will exhibit alower temperature difference from the entering heat-exchange medium thanthat which passes through tube 86. This can be utilized in the presentcase by introducing the part, that was cooled last, to bank of tubes 62at a point where one would expect a higher temperature to start with.This point is usually in the area of the hot spot, such as within aradially internally directed deflecting plate, for example, 100.Accordingly, one allows tube 88 to end in this region, again in anenlargement 102, so that the partial stream of the heat-exchange mediumleaving there can mix with the main stream, the path of which issubstantially that shown by lines 104, which have the arrows.

Naturally, further variations and possible combinations that differ fromthe above are possible.

I claim:
 1. In a tubular reactor for catalytic chemical reactions, withexothermic or endothermic heat of reaction, in which a heat-exchangemedium flows around a bank of reaction tubes extending between tubeplates and is introduced into a reactor housing substantially in anormal direction to the axis of the tubes, and directed from an outsideof the housing in an area near an inlet area of the reaction fluid, theimprovement comprising a continuously open by-pass channel, disposedsubstantially longitudinally centrally within the bank of reactiontubes, conducting a portion of the heat exchange medium which hasentered in close proximity to the tube plate at an inlet side of thereaction fluid through the by-pass channel to an area downstream withregard to the reaction fluid without therebetween contacting thereaction tubes, thus to obtain approximately uniform temperatures withinplanes across the bank of reaction tubes during operation.
 2. In atubular reactor according to claim 1, wherein the reaction tubes aredisposed in the form of a cylindrical bank of tubes and furtherincluding a heat-exchange medium inlet and outlet disposed to direct theheat exchange medium radially with respect to the reaction tubes,wherein there are no reaction tubes at the longitudional center of thebank of reaction tubes, and wherein the by-pass channel consistsessentially of an elongated conduit disposed coaxially in the center ofthe bank of reaction tubes.
 3. In a tubular reactor according to claim 1further including two oppositely disposed banks of reaction tubes,wherein the by-pass channel comprises at least one elongated conduitarranged between the two opposed banks of reaction tubes.
 4. In atubular reactor according to claim 3, wherein the by-pass channelincludes a funnel-like enlargement on one end.
 5. In a tubular reactoraccording to claim 3 wherein the by-pass channel includes a funnel-likeenlargement on both ends.
 6. In a tubular reactor according to claim 1wherein the by-pass channel includes a plurality of coaxial elongatedconduits.
 7. In a tubular reactor according to claim 6 wherein one ormore of the by-pass conduits discharge heat exchange medium in indirectheat exchange contact with the reaction tubes.
 8. In a tubular reactoraccording to claim 6 wherein one or more of the by-pass conduitsdischarge heat exchange medium in a direction toward a deflecting platedisposed within the reactor.
 9. In a method of heating or cooling areaction fluid to provide a proper temperature of reaction for thereaction fluid in catalytic reaction of the reaction fluid comprisingflowing the reaction fluid in an axial flow path through a plurality ofreaction fluid-carrying conduits disposed within a reactor housing, andflowing a heat exchange medium through the reaction housing for indirectheat exchange between the reaction fluid and the heat exchange medium torender a temperature of the reaction fluid suitable for chemicalreaction, the improvement comprising continuously directing anoverheated or, respectively, overcooled inlet portion of the heatexchange medium through an elongated by-pass channel disposedlongitudinally centrally within the reactor such that the by-passedportion of the heat exchange medium does not provide any substantialheat exchange with the reaction fluid.
 10. In the method of claim 9further including directing a portion of the heat exchange mediumsubstantially longitudionally centrally between the reaction tubes toavoid indirect heat exchange between the by-passed heat exchange mediumand the inlet reaction fluid.
 11. In the method of claim 10, furtherincluding directing the by-passed portion of the heat-exchange mediumbetween two oppositely disposed banks of reaction tubes, said by-passchannel including at least one elongated conduit arranged between thetwo opposed banks of reaction tubes.
 12. In the method of claim 10,further including directing the by-passed portion of the heat-exchangemedium through a sieve-like perforated plate disposed near an inlet endof the by-pass channel and in fluid communication with the by-passchannel for the entry of the heat exchange medium into the by-passchannel.
 13. In the method of claim 9 further including directing theby-passed portion of the heat-exchange medium through a plurality ofcoaxial, elongated by-pass conduits.
 14. In the method of claim 13,further including the step of discharging heat exchange medium from oneor more of the coaxial by-pass conduits in indirect heat exchangecontact with the reaction tubes.
 15. In the method of claim 14,including discharging by-passed heat exchange medium from one or more ofthe by-pass conduits in a direction toward a deflecting plate disposedwithin the reactor.
 16. In a method of heating or cooling a reactionfluid to provide a proper temperature of reaction for the reaction fluidcomprising flowing the reaction fluid in an axial flow path through aplurality of reaction fluid-carrying conduits disposed within a reactorhousing, and flowing a heat exchange medium through the reaction housingfor indirect heat exchange between the reaction fluid and the heatexchange medium to render a temperature of the reaction fluid suitablefor chemical reaction, the improvement comprising continuously directingan overheated or, respectively, overcooled inlet portion of the heatexchange medium through an elongated by-pass channel disposed in an areaof the reactor such that the by-passed portion of the heat exchangemedium does not provide any substantial heat exchange with the reactionfluid.
 17. In a tubular reactor for catalytic chemical reactions, withexothermic or endothermic heat of reaction, in which a heat-exchangemedium flows around a bank of reaction tubes and is introduced into areactor housing substantially in a normal direction to the axis of thetubes, and directed from an outside of the housing in an area near aninlet area of the reaction fluid, said reactor housing including aheat-exchange medium inlet and outlet disposed to direct theheat-exchange medium radially with respect to the reaction tubes andsaid reaction tubes being disposed in the form of a cylindrical bank oftubes wherein no reaction tubes are provided at the longitudional centerof the bank of reaction tubes, the improvement comprising a by-passchannel including a funnel-like enlargement on one end, said by-passchannel consisting essentially of an elongated conduit disposedcoaxially in the center of the bank of reaction tubes, by-passing thereaction tubes form an area near the reaction fluid inlet to an areacloser to a reaction fluid outlet, so that a partial stream of theheat-exchange medium in an intermediate area is conveyed through theby-pass channel to provide more uniform heat transfer within thereactor.
 18. In a tubular reactor for catalytic chemical reactions, withexothermic or endothermic heat of reaction, in which a heat-exchangemedium flows around a bank of reaction tubes and is introduced into areactor housing substantially in a normal direction to the axis of thetubes, and directed from an outside of the housing in an area near aninlet area of the reaction fluid, said reactor housing including aheat-exchange medium inlet and outlet disposed to direct theheat-exchange medium radially with respect to the reaction tubes andsaid reaction tubes being disposed in the form of a cylindrical bank oftubes wherein no reaction tubes are provided at the longitudional centerof the bank of reaction tubes, the improvement comprising a by-passchannel including a funnel-like enlargement on both ends, said by-passchannel consisting essentially of an elongated conduit disposedcoaxially in the center of the bank of reaction tubes, by-passing thereaction tubes form an area near the reaction fluid inlet to an areacloser to a reaction fluid outlet, so that a partial stream of theheat-exchange medium in an intermediate area is conveyed through theby-pass channel to provide more uniform heat transfer within thereactor.
 19. In a tubular reactor for catalytic chemical reactions, withexothermic or endothermic heat of reaction, in which a heat-exchangemedium flows around a bank of reaction tubes and is introduced into areactor housing substantially in a normal direction to the axis of thetubes, and directed from an outside of the housing in an area near aninlet area of the reaction fluid, said reactor housing including aheat-exchange medium inlet and outlet disposed to direct theheat-exchange medium radially with respect to the reaction tubes andsaid reaction tubes being disposed in the form of a cylindrical bank oftubes wherein no reaction tubes are provided at the longitudional centerof the bank of reaction tubes, the improvement comprising a by-passchannel including a funnel-like enlargement on one end, said by-passchannel consisting essentially of an elongated conduit disposedcoaxially in the center of the bank of reaction tubes, by-passing thereaction tubes from an area near the reaction fluid inlet to an areacloser to a reaction fluid outlet, so that a partial stream of theheat-exchange medium in an intermediate area is conveyed through theby-pass channel to provide more uniform heat transfer within thereactor, wherein said by-pass channel includes a sieve-like perforatedplate disposed near an inlet end in fluid communication with the by-passchannel for the entry of the heat-exchange medium into the by-passchannel.
 20. In a method of heating or cooling a reaction fluid toprovide a proper temperature of reaction for the reaction fluidcomprising flowing the reaction fluid in an axial flow path through aplurality of reaction fluid-carrying conduits disposed within a reactorhousing, and flowing a heat-exchange medium through the reactor housingfor indirect heat-exchange between the reaction fluid and theheat-exchange medium, the improvement comprising directing an inletportion of the heat-exchange medium through a funnel-like enlargementinto one end of an elongated by-pass channel disposed in an area of thereactor such that the by-passed portion of the heat-exchange medium doesnot provide any substantial heat-exchange with the reaction fluid. 21.In a method of heating or cooling a reaction fluid to provide a propertemperature of reaction for the reaction fluid comprising flowing thereaction fluid in an axial flow path through a plurality of reactionfluid-carrying conduits disposed within a reactor housing, and flowing aheat-exchange medium through the reactor housing for indirectheat-exchange between the reaction fluid and the heat-exchange medium,the improvement comprising directing an inlet portion of theheat-exchange medium through a funnel-like enlargement into one end ofan elongated by-pass channel disposed longitudionally centrally betweenthe reaction fluid-carrying conduits such that the by-pass portion ofthe heat exchange medium does not provide any substantial heat exchangewith the reaction fluid.
 22. In a method of heating or cooling areaction fluid to provide a proper temperature of reaction for thereaction fluid comprising flowing the reaction fluid in an axial flowpath through a plurality of reaction fluid-carrying conduits disposedwithin a reactor housing, and flowing heat-exchange medium through thereactor housing for indirect heat-exchange between the reaction fluidand the heat-exchange medium, the improvement comprising directing aninlet portion of the heat-exchange medium through a funnel-likeenlargement into one end of an elongated by-pass channel disposed in anarea of the reactor such that the by-passed portion of the heat-exchangemedium does not provide any substantial heat-exchange with the reactionfluid and directing an outlet of the by-passed heat-exchange mediumthrough another funnel-like enlargement on the other end of the by-passchannel.
 23. In a method of heating or cooling a reaction fluid toprovide a proper temperature of reaction for the reaction fluidcomprising flowing the reaction fluid in an axial flow path through aplurality of reaction fluid-carrying conduits disposed within a reactionhousing, and flowing a heat-exchange medium through the reactor housingfor indirect heat-exchange between the reaction fluid and theheat-exchange medium, the improvement comprising directing an inletportion of the heat-exchange medium through a funnel-like enlargementinto one end of an elongated by-pass channel disposed longitudionallycentrally between the reaction fluid-carrying conduits such that theby-passed portion of the heat exchange medium does not provide anysubstantial heat exchange with the reaction fluid, and directing anoutlet of the by-passed heat-exchange fluid through another funnel-likeenlargement on the other end of the by-pass channel.
 24. In a method ofheating or cooling a reaction fluid to provide a proper temperature ofreaction for the reaction fluid comprising flowing the reaction fluid inan axial flow path through a plurality of reaction fluid-carryingconduits disposed within a reactor housing, and flowing a heat-exchangemedium through the reactor housing for indirect heat-exchange betweenthe reaction fluid and the heat-exchange medium, the improvementcomprising directing an inlet portion of the heat-exchange mediumthrough a funnel-like enlargement into one end of an elongated by-passchannel disposed longitudionally centrally between the reactionfluid-carrying conduits such that the by-passed portion of the heatexchange medium does not provide any substantially heat exchange withthe reaction fluid, wherein said by-pass channel includes a sieve-likeperforated plate disposed near an inlet end in fluid communication withthe by-pass channel for the entry of the heat-exchange medium int theby-pass channel.